Courtney Lewis, conductor and co-founder of Boston’s Discovery Ensemble, has been named assistant conductor at the New York Philharmonic, a position he will take on starting in September. Lewis, a native of Belfast and current associate conductor of the Minnesota Orchestra, was one of many conductors invited to audition for the position. At the Philharmonic, Lewis will assist Music Director Alan Gilbert and help lead educational events. “It’s very exciting,” said Lewis, 29. “I’ll be conducting the Young People’s concerts and will get a lot of exposure being in New York.” Lewis will continue to lead the Discovery Ensemble, which performs four concerts a year. The ensemble will present “An Embarrassment of Musical Riches,” featuring works by Schubert, Haydn, Berg, and Brahms, Sunday at Jordan Hall.